Dynamics of the middle atmosphere at low, mid and high latitudes observed by the microwave wind radiometer WIRA

Transcription

1 Dynamics of the middle atmosphere at low, mid and high latitudes observed by the microwave wind radiometer WIRA Rolf Rüfenacht, Niklaus Kämpfer, Klemens Hocke, Ansgar Schanz Institute of Applied Physics, University of Bern, Switzerland ARISE final meeting 2014

2 Reasons for developing microwave Doppler wind radiometry

3 The measurement principle Doppler effect: ν = v LOS c ν 0 where v LOS = v cos ɛ with ɛ: elevation angle Frequency ν 0 = GHz from the rotational transition of the ozone molecule 6 khz ˆ 13 m/s

4 The measurement principle Doppler effect: ν = v LOS c ν 0 where v LOS = v cos ɛ with ɛ: elevation angle Frequency ν 0 = GHz from the rotational transition of the ozone molecule 6 khz ˆ 13 m/s Observations from west and east zonal wind Observations from north and south meridional wind Ozone emission line is pressure broadened altitude information

5 The instrument

6 The instrument Backend (in lab) Frontend (outdoors) AFFTS spectrometer Board GHz resolution: 6.1 khz bandwidth: 100 MHz x8 10 MHz ref. active mult GHz Board 2 10 MHz ref GHz resolution: 183 khz bandwidth: 1500 MHz

7 The instrument Backend (in lab) Frontend (outdoors) AFFTS spectrometer Board GHz resolution: 6.1 khz bandwidth: 100 MHz x8 10 MHz ref. active mult GHz Board 2 10 MHz ref GHz resolution: 183 khz bandwidth: 1500 MHz 154 west east Brightness temperature [K] Frequency [GHz]

8 The retrieval principle west east 150 Brightness temperature [K] Frequency [GHz] Atmospheric emission spectra Zonal wind [m/s] Wind profile

9 The retrieval principle west east 150 Brightness temperature [K] Frequency [GHz] Atmospheric emission spectra Zonal wind [m/s] Wind profile

10 The retrieval principle west east 150 Brightness temperature [K] Frequency [GHz] Atmospheric emission spectra Optimal estimation technique Zonal wind [m/s] Wind profile Based on the measurement, a priori knowledge and uncertainties

11 Altitude resolution and accuracy Altitude resolution [km] Altitude accuracy [km] Measurement response Approx. altitude [km]

12 Error analysis 10 3 Noise level 0.1 K 10 3 True wind profile Standard retrieval Peak frequency Line intensity Pressure broad. coeff. p broad. T dependence Temperature profile Noise level 0.2 K

13 Zonal wind measured in Sodankylä (Oct Jul 2012) Polar latitudes (67 22 N / E) Zonal wind WIRA Oct 13 Dec 01 Feb 22 Mar 11 May 30 Jun Zonal wind ECMWF Oct 13 Dec 01 Feb 22 Mar 11 May 30 Jun 50

14 Zonal wind measured in Bern (Sep Jul 2011) Mid latitudes (46 57 N / 7 26 E) Zonal wind WIRA Sep 08 Nov 28 Dec 16 Feb 07 Apr 27 May 16 Jul 50 Zonal wind ECMWF Sep 08 Nov 28 Dec 16 Feb 07 Apr 27 May 16 Jul 50

15 Zonal wind measured in Provence (Nov May 2013) Mid latitudes (43 56 N / 5 43 E) Zonal wind WIRA Nov 17 Dec 06 Jan 26 Jan 15 Feb 07 Mar 27 Mar 16 Apr 06 May Zonal wind ECMWF Nov 17 Dec 06 Jan 26 Jan 15 Feb 07 Mar 27 Mar 16 Apr 06 May 50

16 Meridional wind measured in Provence (Nov 12 - May 13) Mid latitudes (43 56 N / 5 43 E) Meridional wind WIRA 27 Nov 17 Dec 06 Jan 26 Jan 15 Feb 07 Mar 27 Mar 16 Apr 06 May Meridional wind ECMWF 27 Nov 17 Dec 06 Jan 26 Jan 15 Feb 07 Mar 27 Mar 16 Apr 06 May

17 Zonal wind measured on La Réunion (Sep 13 - Nov 14) Tropical latitudes (21 04 S / E) Zonal wind WIRA Sep 12 Nov 01 Jan 20 Feb 11 Apr 31 May 20 Jul 08 Sep 28 Oct 100 Zonal wind ECMWF Sep 12 Nov 01 Jan 20 Feb 11 Apr 31 May 20 Jul 08 Sep 28 Oct 100

18 27 day wave and link to solar activity? Zonal wind on La Réunion correlated with solar Lyman-alpha irradiance Correlation coefficient Time lag [days] 0.5

19 27 day wave and link to solar activity? Meridional wind on La Réunion correlated with solar Lyman-alpha irradiance Correlation coefficient Time lag [days] 0.5

20 Conclusions and outlook Continuous middle-atmospheric wind measurements (by microwave radiometry) offer a number of opportunities for atmospheric research: Direct observations of dynamical phenomena: Seasonal cycle Sudden stratospheric warmings Behaviour of the polar vortex Tropical patterns like semi-annual oscillation and potentially quasi-biennial oscillation Studies of atmospheric waves (like the 27 day wave)

21 Conclusions and outlook Continuous middle-atmospheric wind measurements (by microwave radiometry) offer a number of opportunities for atmospheric research: Direct observations of dynamical phenomena: Seasonal cycle Sudden stratospheric warmings Behaviour of the polar vortex Tropical patterns like semi-annual oscillation and potentially quasi-biennial oscillation Studies of atmospheric waves (like the 27 day wave) New compact WIRA-C is under construction to be used in ARISE-2

22 Averaging kernels 10 3 Averaging kernels Measurement response /

23 Error analysis 10 3 Noise level 0.1 K 10 3 True wind profile Standard retrieval O3 variation O3 var. large O3 var. small Baseline 1 Baseline 2 Baseline Baseline 4 Noise level 0.2 K

24 Dependence from a priori information A priori profile 0 m/s 10 m/s 10 m/s 20 m/s 20 m/s 30 m/s 30 m/s 40 m/s 40 m/s 50 m/s 50 m/s Approx. altitude [km] Zonal wind speed [m/s]

25 Position of polar vortex edge vs Sodankylä (winter 2011/12) Figure from Dominik Scheiben

26 Strength of polar vortex (winter 2011/12) Figure from Dominik Scheiben